Electro-optical device and electronic device

ABSTRACT

An object of the present invention is to provide an EL display device, which has a high operating performance and reliability.  
     A third passivation film  45  is disposed under an EL element  203  which comprises a pixel electrode (anode)  46 , an EL layer  47  and a cathode  48 , to make a structure in which heat generated by the EL element  203  is radiated. Further, the third passivation film  45  prevents alkali metals within the EL element  203  from diffusing into the TFTs side, and prevents moisture and oxygen of the TFTs side from penetrating into the EL element  203 . More preferably, heat radiating effect is given to a fourth passivation film  50  to make the EL element  203  to be enclosed by heat radiating layers.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electro-optical device,typically an EL (electroluminescence) display device formed by asemiconductor element (an element using a semiconductor thin film) madeon a substrate, and to electronic equipment (an electronic device)having the electro-optical device as a display (also referred to as adisplay portion).

[0003] 2. Description of the Related Art

[0004] Techniques of forming a TFT on a substrate have been widelyprogressing in recent years, and developments of applications to anactive matrix type display device are advancing. In particular, a TFTusing a polysilicon film has a higher electric field effect mobility(also referred to as mobility) than a TFT using a conventional amoroussilicon film, and high speed operation is therefore possible. As aresult, it becomes possible to perform pixel control, conventionallyperformed by a driver circuit external to the substrate, by a drivercircuit formed on the same substrate as the pixel.

[0005] This type of active matrix display device has been in thespotlight because of the many advantage which can be obtained byincorporating various circuits and elements on the same substrate inthis type of active matrix display device, such as reduced manufacturingcost, small size, increased yield, and higher throughput.

[0006] An EL layer (light emitting layer) is made to emit light in anactive matrix EL display device by disposing a switching element formedfrom a TFT to each pixel, and by driving a driver element that performscurrent control by the switching element. For example, there are ELdisplay devices disclosed in U.S. Pat. No. 5,684,365 (Japanese PatentApplication Laid-Open No. Hei 8-234683) and Japanese Patent ApplicationLaid-Open No. Hei 10-189252.

[0007] Degradation of EL materials due to moisture has been a problem inthese EL display devices. Specifically organic EL materials degrade notonly by moisture but also by oxygen. Accordingly EL elements aregenerally shielded from moisture, etc., by sealing the EL elements asdisclosed in Japanese Patent Application Laid-Open No. Hei 8-78159.

[0008] However, the problem that the EL layer has is not limited tomoisture. The EL layer includes alkaline metals such as sodium (Na) initself, and a serious trouble can be caused to the operation of TFTswhen the alkali metals are diffused into the TFTs. Further, degradationdue to storage of heat is also a problem because an EL layer is weak toheat. Note that alkaline metals are referred to ‘alkaline metals’ toinclude alkali earth metals through the Specification.

SUMMARY OF THE INVENTION

[0009] In view of the above conventional technique, an object of thepresent invention is to provide an electro-optical device having goodoperation performance and high reliability, and in particular, toprovide an EL display device. Another object of the present invention isto increase the quality of electronic equipment (an electronic device)having the electro-optical device as a display by increasing the imagequality of the electro-optical device.

[0010] In order to achieve the above objects, degradation of EL elementsdue to moisture, degradation due to heat and release of alkaline metalsare prevented in the present invention. In concrete, an insulating filmwhich satisfies these is disposed in contact with the EL elements, ormore preferably the EL elements are enclosed by such insulating films.

[0011] Namely, an insulating film, which has a blocking effect ofmoisture and alkaline metals, and a heat radiating effect is disposed toa nearest position to the EL elements, and degradation of the Elelements is suppressed by the insulating film.

[0012] Note that a laminate of an insulating film having blocking effectagainst moisture and alkaline metals and an insulating film having heatradiating effect can be used in case that such insulating film cannot beused by a single layer. Further, it is possible to use laminate of aninsulating film having blocking effect against moisture, an insulatingfilm having blocking effect against alkaline metals and an insulatingfilm having heat radiating effect.

[0013] In either way, measures against both of moisture and heat shouldbe sought in order to suppress degradation of the EL layer (it may alsobe referred to as degradation of EL element), and it is necessary totake measures against heat, moisture and alkaline metals for the TFTsthemselves that driver the EL elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the accompanying drawings:

[0015]FIG. 1 is a diagram showing the cross sectional structure of thepixel portion of an EL display device;

[0016]FIGS. 2A and 2B are diagrams showing the top view and thecomposition, respectively, of the pixel portion of an EL display device;

[0017]FIGS. 3A to 3E are diagrams showing manufacturing processes of anactive matrix type EL display device;

[0018]FIGS. 4A to 4D are diagrams showing manufacturing processes of anactive matrix type EL display device;

[0019]FIGS. 5A to 5C are diagrams showing manufacturing processes of anactive matrix type EL display device;

[0020]FIG. 6 is a diagram showing an external view of an EL module;

[0021]FIG. 7 is a diagram showing the circuit block structure of an ELdisplay device;

[0022]FIG. 8 is an enlarged diagram of the pixel portion of an ELdisplay device;

[0023]FIG. 9 is a diagram showing the element structure of a samplingcircuit of an EL display device;

[0024]FIG. 10 is a diagram showing the composition of the pixel portionof an EL display device;

[0025]FIG. 11 is a diagram showing the cross sectional structure of anEL display device;

[0026]FIGS. 12A and 12B are diagrams showing the top view and thecomposition, respectively, of the pixel portion of an EL display device;

[0027]FIG. 13 is a diagram showing the cross sectional structure of thepixel portion of an EL display device;

[0028]FIG. 14 is a diagram showing the cross sectional structure of thepixel portion of an EL display device;

[0029]FIGS. 15A and 15B are diagrams showing the top view and thecomposition, respectively, of the pixel portion of an EL display device;

[0030]FIGS. 16A to 16F are diagrams showing specific examples ofelectronic equipment;

[0031]FIGS. 17A and 17B are diagrams showing external views of an ELmodule;

[0032]FIGS. 18A to 18C are diagrams showing manufacturing processes of acontact structure;

[0033]FIG. 19 is a diagram showing the laminate structure of an ELlayer;

[0034]FIGS. 20A and 20B are diagrams showing specific examples ofelectronic equipment;

[0035]FIGS. 21A and 21B are diagrams showing the circuit composition ofthe pixel portion of an EL display device;

[0036]FIGS. 22A and 22B are diagrams showing the circuit composition ofthe pixel portion of an EL display device; and

[0037]FIG. 23 is a diagram showing the cross sectional structure of thepixel portion of an EL display device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Embodiment Mode

[0039] FIGS. 1 to 2B are used in explaining the preferred embodiments ofthe present invention. Shown in FIG. 1 is a cross sectional diagram of apixel of an EL display device of the present invention, in FIG. 2A isits top view, and in FIG. 2B is a circuit composition. In practice, apixel portion (image display portion) is formed with a multiple numberof this type of pixel arranged in a matrix state.

[0040] Note that the cross sectional diagram of FIG. 1 shows a crosssection cut along the line A-A′ in the top view shown in FIG. 2A. Commonsymbols are used in FIG. 1 and in FIGS. 2A and 2B, and therefore thethree figures may be referenced as appropriate. Furthermore, two pixelsare shown in the top view of FIG. 2A, and both have the same structure.

[0041] Reference numeral 11 denotes a substrate, and reference numeral12 denotes a base film in FIG. 1. A glass substrate, a glass ceramicsubstrate, a quartz substrate, a silicon substrate, a ceramic substrate,a metallic substrate, or a plastic substrate (including a plastic film)can be used as the substrate 11.

[0042] Further, the base film 12 is especially effective for cases inwhich a substrate containing mobile ions, or a substrate havingconductivity, is used, but need not be formed for a quartz substrate. Aninsulating film containing silicon may be formed as the base film 12.Note that the term “insulating film containing silicone” indicates,specifically, an insulating film that contains silicon, oxygen, andnitrogen in predetermined ratios such as a silicon oxide film, a siliconnitride film, or a silicon oxynitride film (denoted by SiO_(x)N_(y)).

[0043] Note that it is also effective to prevent degradation of TFTs orEL elements by giving heat radiating effect to the base film 12 andradiate heat generated from TFTs. All known materials can be used forgiving heat radiating effect.

[0044] Two TFTs are formed within the pixel here. Reference numeral 201denotes a TFT functioning as a switching element (hereafter referred toas a switching TFT), and reference numeral 202 denotes a TFT functioningas a current control element for controlling the amount of currentflowing to an EL element (hereafter referred to as a current controlTFT), and both are formed by an n-channel TFT.

[0045] The field effect mobility of the n-channel TFT is larger than thefield effect mobility of a p-channel TFT, and therefore the operationspeed is fast and electric current can flow easily. Further, even withthe same amount of current flow, the n-channel TFT can be made smaller.The effective surface area of the display portion therefore becomeslarger when using the n-channel TFT as a current control TFT, and thisis preferable.

[0046] The p-channel TFT has the advantages that hot carrier injectionessentially does not become a problem, and that the off current value islow, and there are already reports of examples of using the p-channelTFT as a switching TFT and as a current control TFT. However, by using astructure in which the position of an LDD region differs, the problemsof hot carrier injection and the off current value in the n-channel TFTare solved by the present invention. The present invention ischaracterized by the use of n-channel TFTs for all of the TFTs withinall of the pixels.

[0047] Note that it is not necessary to limit the switching TFT and thecurrent control TFT to n-channel TFTs in the present invention, and thatit is possible to use p-channel TFTs for either the switching TFT, thecurrent control TFT, or both.

[0048] The switching TFT 201 is formed having: an active layercomprising a source region 13, a drain region 14, LDD regions 15 a to 15d, a high concentration impurity region 16, and channel forming regions17 a and 17 b; a gate insulating film 18; gate electrodes 19 a and 19 b,a first interlayer insulating film 20, a source wiring 21, and a drainwiring 22.

[0049] As shown in FIG. 2A, the gate electrodes 19 a and 19 b become adouble gate structure electrically connected by a gate wiring 211 whichis formed by a different material (a material having a lower resistancethan the gate electrodes 19 a and 19 b). Of course, not only a doublegate structure, but a so-called multi-gate structure (a structurecontaining an active layer having two or more channel forming regionsconnected in series), such as a triple gate structure, may also be used.The multi-gate structure is extremely effective in lowering the value ofthe off current, and by making the switching TFT 201 of the pixel into amulti-gate structure with the present invention, a low off current valuecan be realized for the switching TFT.

[0050] The active layer is formed by a semiconductor film containing acrystal structure. In other words, a single crystal semiconductor filmmay be used, and a polycrystalline semiconductor film or amicrocrystalline semiconductor film may also be used. Further, the gateinsulating film 18 may be formed by an insulating film containingsilicon. Additionally, a conducting film can be used for all of the gateelectrodes, the source wiring, and the drain wiring.

[0051] In addition, the LDD regions 15 a to 15 d in the switching TFT201 are formed so as not to overlay with the gate electrodes 19 a and 19b by interposing the gate insulating film 18. This structure isextremely effective in reducing the off current value.

[0052] Note that the formation of an offset region (a region thatcomprises a semiconductor layer having the same composition as thechannel forming regions, and to which a gate voltage is not applied)between the channel forming regions and the LDD regions is morepreferable for reducing the off current value. Further, when amulti-gate structure having two or more gate electrodes is used, thehigh concentration impurity region formed between the channel formingregions is effective in lowering the value of the off current.

[0053] By thus using the multi-gate structure TFT as the switching TFT201, as above, a switching element having a sufficiently low off currentvalue is realized by the present invention. The gate voltage of thecurrent control TFT can therefore be maintained for a sufficient amountof time (for a period from one selection until the next selection)without forming a capacitor, such as the one stated in the FIG. 2 ofJapanese Patent Application Laid-Open No. 10-189252.

[0054] Namely, it becomes possible to eliminate the capacitor whichcauses a reduction in the effective luminescence surface area, and itbecomes possible to increase the effective luminescence surface area.This means that the image quality of the EL display device can be madebrighter.

[0055] Next, the current control TFT 202 is formed having: an activelayer comprising a source region 31, a drain region 32, an LDD region33, and a channel forming region 34; a gate insulating film 18; a gateelectrode 35; the first interlayer insulating film 20; a source wiring36; and a drain wiring 37. Note that the gate electrode 35 has a singlegate structure, but a multi-gate structure may also be used.

[0056] As shown in FIGS. 2A and 2B, the drain of the switching TFT 201is electrically connected to the gate of the current control TFT 202.Specifically, the gate electrode 35 of the current control TFT 202 iselectrically connected to the drain region 14 of the switching TFT 201through the drain wiring (also referred to as a connection wiring) 22.Further, the source wiring 36 is connected to an electric current supplywiring 212.

[0057] A characteristic of the current control TFT 202 is that itschannel width is larger than the channel width of the switching TFT 201.Namely, as shown in FIG. 8, when the channel length of the switching TFTis taken as L1 and its channel width as W1, and the channel length ofthe current control TFT is taken as L2 and its channel width as W2, arelational expression is reached in which W2/L2≧5×W1/L1 (preferablyW2/L2≧10×W1/L1). Consequently, it is possible for more current to easilyflow in the current control TFT than in the switching TFT.

[0058] Note that the channel length L1 of the multi-gate structureswitching TFT is the sum of each of the channel lengths of the two ormore channel forming regions formed. A double gate structure is formedin the case of FIG. 8, and therefore the sum of the channel lengths L1aand L1b, respectively, of the two channel-forming regions becomes thechannel length L1 of the switching TFT.

[0059] The channel lengths L1 and L2, and the channel widths W1 and W2are not specifically limited to a range of values with the presentinvention, but it is preferable that W1 be from 0.1 to 5 μm (typicallybetween 1 and 3 μm), and that W2 be from 0.5 to 30 μm (typically between2 and 10 μm). It is preferable that L1 be from 0.2 to 18 μm (typicallybetween 2 and 15 μm), and that L2 be from 0.1 to 50 μm (typicallybetween 1 and 20 μm) at this time.

[0060] Note that it is preferable to set the channel length L in thecurrent control TFT on the long side in order to prevent excessivecurrent flow. Preferably, W2/L2≧3 (more preferably W2/L2≧5). It is alsopreferable that the current flow per pixel is from 0.5 to 2 μA (betterbetween 1 and 1.5 μA).

[0061] By setting the numerical values within this range, all standards,from an EL display device having a VGA class number of pixels (640×480)to an EL display device having a high vision class number of pixels(1920×1080) can be included.

[0062] Furthermore, the length (width) of the LDD region formed in theswitching TFT 201 is set from 0.5 to 3.5 μm, typically between 2.0 and2.5 μm.

[0063] The EL display device shown in FIG. 1 is characterized in thatthe LDD region 33 is formed between the drain region 32 and the channelforming region 34 in the current control TFT 202. In addition, the LDDregion 33 has both a region which overlaps, and a region which does notoverlap the gate electrode 35 by interposing a gate insulating film 18.

[0064] The current control TFT 202 supplies a current for making the ELelement 203 luminesce, and at the same time controls the amount suppliedand makes gray scale display possible. It is therefore necessary thatthere is no deterioration when the current flows, and that steps aretaken against deterioration due to hot carrier injection. Furthermore,when black is displayed, the current control TFT 202 is set in the offstate, but if the off current value is high, then a clean black colordisplay becomes impossible, and this invites problems such as areduction in contrast. It is therefore necessary to suppress the valueof the off current.

[0065] Regarding deterioration due to hot carrier injection, it is knownthat a structure in which the LDD region overlaps the gate electrode isextremely effective. However, if the entire LDD region is made tooverlap the gate electrode, then the value of the off current rises, andtherefore the applicant of the present invention resolves both the hotcarrier and off current value countermeasures at the same time by anovel structure in which an LDD region which does not overlap the gateelectrode is formed in series.

[0066] The length of the LDD region which overlaps the gate electrodemay be made from 0.1 to 3 μm (preferable between 0.3 and 1.5 μm) at thispoint. If it is too long, then the parasitic capacitance will becomelarger, and if it is too short, then the effect of preventing hotcarrier will become weakened. Further, the length of the LDD region notoverlapping the gate electrode may be set from 1.0 to 3.5 μm (preferablebetween 1.5 and 2.0 μm). If it is too long, then a sufficient currentbecomes unable to flow, and if it is too short, then the effect ofreducing off current value becomes weakened.

[0067] A parasitic capacitance is formed in the above structure in theregion where the gate electrode and the LDD region overlap, andtherefore it is preferable that this region not be formed between thesource region 31 and the channel forming region 34. The carrier(electrons in this case) flow direction is always the same for thecurrent control TFT, and therefore it is sufficient to form the LDDregion on only the drain region side.

[0068] Further, looking from the viewpoint of increasing the amount ofcurrent that is able to flow, it is effective to make the film thicknessof the active layer (especially the channel forming region) of thecurrent control TFT 202 thick (preferably from 50 to 100 nm, morepreferably between 60 and 80 nm). Conversely, looking from the point ofview of making the off current value smaller for the switching TFT 201,it is effective to make the film thickness of the active layer(especially the channel forming region) thin (preferably from 20 to 50nm, more preferably between 25 and 40 nm).

[0069] Next, reference numeral 41 denotes a first passivation film, andits film thickness may be set from 10 nm to 1 μm (preferably between 200and 500 nm). An insulating film containing silicon (in particular,preferably a silicon oxynitride film or a silicon nitride film) can beused as the passivation film material. The passivation film 41 plays therole of protecting the manufactured TFT from alkaline metals andmoisture. Alkaline metals such as sodium are contained in an EL layerformed on the final TFT. In other words, the first passivation film 41works as a protecting layer so that these alkaline metals (mobile ions)do not penetrate into the TFT. Note that alkaline metals andalkaline-earth metals are contained in the term ‘alkaline metal’throughout this specification.

[0070] Further, by making the passivation film 41 possess a heatradiation effect, it is also effective in preventing thermal degradationof the EL layer. Note that light is emitted from the base 11 side in theFIG. 1 structure of the EL display device, and therefore it is necessaryfor the passivation film 41 to have light transmitting characteristics.Further, it is preferable not to use an insulating film which is apt torelease oxygen in the case of using an organic material as the EL layerbecause it degrades by bonding with oxygen.

[0071] An insulating film comprising at least one element selected fromthe group consisting of B (boron), C (carbon), and N (nitrogen), and atleast one element selected from the group consisting of Al (aluminum),Si (silicon), and P (phosphorous) can be given as a light transparentmaterial possessing heat radiation qualities (having high heatconductivity). For example, it is possible to use: an aluminum nitridecompound, typically aluminum nitride (Al_(x)N_(y)); a silicon carbidecompound, typically silicon carbide (Si_(x)C_(y)); a silicon nitridecompound, typically silicon nitride (Si_(x)N_(y)); a boron nitridecompound, typically boron nitride (B_(x)N_(y)); or a boron phosphatecompound, typically boron phosphate (B_(x)P_(y)). Further, an aluminumoxide compound, typically aluminum oxide (Al_(x)O_(y)), has superiorlight transparency characteristics, and has a thermal conductivity of 20Wm⁻¹K⁻¹, and can be said to be a preferable material. These materialsnot only possess heat radiation qualities, but also are effective inpreventing the penetration of substances such as moisture and alkalinemetals. Note that x and y are arbitrary integers for the abovetransparent materials.

[0072] The above chemical compounds can also be combined with anotherelement. For example, it is possible to use nitrated aluminum oxide,denoted by AlN_(x)O_(y), in which nitrogen is added to aluminum oxide.This material also not only possesses heat radiation qualities, but alsois effective in preventing the penetration of substances such asmoisture and alkaline metals. Note that x and y are arbitrary integersfor the above nitrated aluminum oxide.

[0073] Furthermore, the materials recorded in Japanese PatentApplication Laid-open No. Sho 62-90260 can also be used. Namely, achemical compound containing Si, Al, N, O, and M can also be used (notethat M is a rare-earth element, preferably an element selected from thegroup consisting of Ce (cesium), Yb (ytterbium), Sm (samarium), Er(erbium), Y (yttrium), La (lanthanum), Gd (gadolinium), Dy (dysprosium),and Nd (neodymium)). These materials not only possess heat radiationqualities, but also are effective in preventing the penetration ofsubstances such as moisture and alkaline metals.

[0074] Furthermore, carbon films containing at least a diamond thin filmor amorphous carbons (especially those which have characteristics closeto those of diamond; referred to as diamond-like carbon) can also beused. These have very high thermal conductivities, and are extremelyeffective as radiation layers. Note that if the film thickness becomeslarger, there is brown banding and the transmissivity is reduced, andtherefore it is preferable to use as thin a film thickness (preferablybetween 5 and 100 nm) as possible.

[0075] Note that the aim of the first passivation film 41 is inprotecting the TFT from alkaline metals and from moisture, and thereforeit must made so as to not lose this effect. A thin film made from amaterial possessing the above radiation effect can be used by itself,but it is effective to laminate this thin film and a thin film havingshielding properties against alkaline metals and moisture (typically asilicon nitride film (Si_(x)N_(y)) or a silicon oxynitride film(SiO_(x)N_(y))). Note that x and y are arbitrary integers for the abovesilicon nitride films and silicon oxynitride films.

[0076] Reference numeral 42 denotes a color filter, and referencenumeral 43 denotes a fluorescent substance (also referred to as afluorescent pigment layer). Both are a combination of the sam color, andcontain red (R), green (G), or blue (B). The color filter 42 is formedin order to increase the color purity, and the fluorescent substance 43is formed in order to perform color transformation.

[0077] Note that EL display devices are roughly divided into four typesof color displays: a method of forming three types of EL elementscorresponding to R, G, and B; a method of combining white colorluminescing EL elements with color filters; a method of combining blueor blue-green luminescing EL elements and fluorescent matter(fluorescing color change layer, CCM); and a method of using atransparent electrode as a cathode (opposing electrode) and overlappingEL elements corresponding to R, G, and B.

[0078] The structure of FIG. 1 is an example of a case of using acombination of blue luminescing EL elements and a fluorescent substance.A blue color emitting luminescence layer is used as the EL element 203here, light possessing blue color region wavelength, includingultraviolet light, is formed, and the fluorescent substance 43 isactivated by the light, and made to emit red, green, or blue light. Thecolor purity of the light is increased by the color filter 42, and thisis outputted.

[0079] Note that it is possible to implement the present inventionwithout being concerned with the method of luminescence, and that allfour of the above methods can be used with the present invention.

[0080] Furthermore, after forming the color filter 42 and thefluorescent substance 43, leveling is performed by a second interlayerinsulating film 44. A resin film is preferable as the second interlayerinsulating film 44, and one such as polyimide, polyamide, acrylic, orBCB (benzocyclobutane) may be used. An inorganic film may, of course,also be used, provided that sufficient leveling is possible.

[0081] The leveling of steps due to the TFT by the second interlayerinsulating film 44 is extremely important. The EL layer formed afterwardis very thin, and therefore there are cases in which poor luminescenceis caused by the existence of a step. It is therefore preferable toperform leveling before forming a pixel electrode so as to be able toform the EL layer on as level a surface as possible.

[0082] Furthermore, reference numeral 45 is a second passivation film(it has a meaning of heat radiating layer), and the film thickness of 5nm to 1 μm (typically between 20 and 300 nm) is preferable. This secondpassivation film is disposed in contact with the EL element, andfunctions to release the heat generated by the EL element, so that heatis not stored in the EL element. Further, when formed by a resin film,the second interlayer insulating film 44 is weak with respect to heat,and the thermal radiation layer works so as not to impart bad influencedue to the heat generated by the EL element.

[0083] It is effective to perform leveling of the TFT by the resin filmin manufacturing the EL display device, as stated above, but there hasnot been a conventional structure which considers the deterioration ofthe resin film due to heat generated by the EL element. It can be saidthat solving that point by disposing the second passivation film 45 isone of the characteristics of the present invention.

[0084] Further, the second passivation film 45 function as a protectionlayer for not diffusing alkaline metals within the EL layer to the TFTsside as well as preventing the above stated degradation due to heat, andstill further functions as a protection layer that prevents penetrationof moisture or oxygen from TFT side to the EL layer.

[0085] The same materials as those used as the first passivation film 41can be used as the second passivation film 45. In particular, asmaterials having high heat radiating effect, a carbon film such as adiamond film or a diamond-like carbon film is preferable, and in orderto prevent penetration of substances such as moisture, it is morepreferable to use a lamination structure of a carbon film and a siliconnitride film (or a silicon oxynitride film).

[0086] A structure in which TFT side and EL element side are segregatedby an insulating film which has a high radiation effect and is capableof shielding moisture and alkaline metal, is an important characteristicof the present invention, and it can be said that it is a structure thatdid not exist in a conventional EL display device.

[0087] Reference numeral 46 denotes a pixel electrode (EL element anode)made from a transparent conducting film. After opening a contact hole inthe second passivation film 45, in the second interlayer insulating film44 and in the first passivation film 41, the pixel electrode 45 isformed so as to be connected to the drain wiring 37 of the currentcontrol TFT 202.

[0088] An EL layer (an organic material is preferable) 47, a cathode 48,and a protecting electrode 49 are formed in order on the pixel electrode46. A single layer structure or a lamination structure can be used asthe EL layer 47, but there are many cases in which the laminationstructure is used. Various lamination structures have been proposed,combinations of layers such as a luminescence layer, an electrontransporting layer, an electron injecting layer, a hole injecting layer,and a hole transporting layer, but any structure may be used for thepresent invention. Doping of a fluorescent pigment into the EL layer mayalso be performed, of course. Note that a luminescing element formed bya pixel electrode (anode), an EL layer, and a cathode is referred to asan EL element throughout this specification.

[0089] All already known EL materials can be used by the presentinvention. Organic materials are widely known as such materials, andconsidering the driver voltage, it is preferable to use an organicmaterial. For example, the materials disclosed in the following U.S.Patents and Japanese patent applications can be used as the organic ELmaterial:

[0090] U.S. Pat. Nos. 4,356,429; 4,539,507; 4,720,432; 4,769,292;4,885,211; 4,950,950; 5,059,861; 5,047,687; 5,073,446; 5,059,862;5,061,617; 5,151,629; 5,294,869; 5,294,870; Japanese Patent ApplicationLaid-open No. Hei 10-189525; Japanese Patent Application Laid-open No.Hei 8-241048; and Japanese Patent Application Laid-open No. Hei 8-78159.

[0091] Specifically, an organic material such as the one shown by thefollowing general formula can be used as a hole injecting layer.

[0092] Here, Q is either N or a C—R (carbon chain); M is a metal, ametal oxide, or a metal halide; R is hydrogen, an alkyl, an aralkyl, anaryl, or an alkalyl; and T1 and T2 are unsaturated six member ringsincluding substituent such as hydrogen, alkyl, or halogen.

[0093] Furthermore, an aromatic tertiary amine can be used as an organicmaterial hole transporting layer, preferably including thetetraaryldiamine shown by the following general formula.

[0094] In Chem 2 Are is an arylene group, n is an integer from 1 to 4,and Ar, R₇, R₈, and R₉ are each various chosen aryl groups.

[0095] In addition, a metal oxynoid compound can be used as an organicmaterial EL layer, electron transporting layer, or electron injectinglayer. A material such as that shown by the general formula below may beused as the metal oxinoid compound.

[0096] It is possible to substitute R₂ through R₇, and a metal oxinoidsuch as the following can also be used.

[0097] In Chem 4, R₂ through R₇ are defined as stated above; L₁ throughL₅ are carbohydrate groups containing from 1 to 12 carbon elements; andboth L₁ and L₂, or both L₂ and L₃ are formed by benzo-rings. Further, ametal oxinoid such as the following may also be used.

[0098] It is possible to substitute R₂ through R₆ here. Coordinationcompounds having organic ligands are thus included as organic ELmaterials. Note that the above examples are only some examples oforganic EL materials which can be used as the EL material of the presentinvention, and that there is absolutely no need to limit the EL materialto these.

[0099] Furthermore, when using an ink jet method for forming the ELlayer, it is preferable to use a polymer material as the EL material.Polymer materials such as the following can be given as typical polymermaterials: polyparaphenylene vinylenes (PPVs); and polyfluorenes. Forcolorization, it is preferable to use, for example, acyano-polyphenylene vinylene in a red luminescing material; apolyphenylene vinylene in a green luminescing material; and apolyphenylene vinylene and a polyalkylphenylene in a blue luminescingmaterial. Regarding organic EL materials which can be used in an ink-jetmethod, all of the materials recorded in Japanese Patent ApplicationLaid-open No. Hei 10-012377 can be cited.

[0100] Furthermore, a material containing a low work coefficientmaterial such as magnesium (Mg), lithium (Li), cesium (Cs), barium (Ba),potassium (K), beryllium (Be), or calcium (Ca) is used as the cathode48. Preferably, an electrode made from MgAg (a material made from Mg andAg at a mixture of Mg:Ag=10:1) may be used. In addition, a MgAgAlelectrode, a LiAl electrode, and a LiFAl electrode can be given as otherexamples. Further, the protecting electrode 49 is an electrode formed inorder to be a protecting film against moisture from external to thecathode 48, and a material containing aluminum (Al) or silver (Ag) isused. The protecting electrode 49 also has a heat radiation effect.

[0101] Note that it is desirable to form the EL layer 47 and the cathode48 in succession, without exposure to the atmosphere. In other words, nomatter what type of lamination structure the EL layer and the cathodecontain, it is preferable to form everything in a multi-chamber (alsoreferred to as a cluster tool) type deposition device in succession.This is in order to avoid the absorption of moisture when the EL layeris exposed to the atmosphere because if an organic material is used asthe EL layer, then it is extremely weak with respect to moisture. Inaddition, not only the EL layer 47 and the cathode 48, it is even betterto form all the way through the protecting electrode 49 in succession.

[0102] The EL layer is extremely weak with respect to heat, andtherefore it is preferable to use vacuum evaporation (in particular, anorganic molecular beam evaporation method is effective in that it formsa very thin film, on the molecular order level), sputtering, plasma CVD,spin coating, screen printing, or ion plating as the film depositionmethod. It is also possible to form the EL layer by an ink-jet method.For the ink jet method there is a bubble jet method using cavitation(refer to Japanese Patent Application Laid-open No. Hei 5-116297), andthere is a piezo method using a piezo element (refer to Japanese PatentApplication Laid-open No. Hei 8-290647), and in view of the fact thatorganic EL materials are weak with respect to heat, the piezo method ispreferable.

[0103] Reference numeral 50 denotes a third passivation film, and itsfilm thickness may be set from 10 nm to 1 μm (preferable between 200 and500 nm). The object of forming the third passivation film 50 is mainlyto protect the EL layer 47 from moisture, but it is also good if thethird passivation film 50 is made to possess a heat radiation effect,similar to the first passivation film 41. The same materials as used forthe first passivation film 41 can therefore be used as the formationmaterial of the third passivation film 50. Note that when an organicmaterial is used as the EL layer 47, it is possible that the EL layerdeteriorates due to bonding with oxygen, and therefore it is preferableto use an insulating film which does not easily emit oxygen.

[0104] Further, the EL layer is weak with respect to heat, as statedabove, and therefore it is preferable to perform film deposition at alow temperature as possible (preferably in the range from roomtemperature to 120° C.). It can therefore be said that plasma CVD,sputtering, vacuum evaporation, ion plating, and solution application(spin coating) are desirable film deposition methods.

[0105] Though the degradation of EL elements can be sufficientlysuppressed by only disposing the second passivation film 45 as statedabove, more preferably the EL elements are enclosed by 2 layers ofinsulating films that are formed to sandwich the EL elements, like asthe second passivation film 45 and the third passivation film 50, andpenetration of moisture and oxygen into the EL layer, diffusion ofalkaline metals from the EL layer, and storage of heat in the EL layerare prevented. As a result, the degradation of the EL layer is furthersuppressed, and an EL display device having high reliability can beobtained.

[0106] The EL display device of the present invention has a pixelportion containing a pixel with a structure of FIG. 1, and TFTs havingdiffering structures in response to their function are arranged in thepixel. A switching TFT having a sufficiently low off current value, anda current control TFT which is strong with respect to hot carrierinjection can be formed within the same pixel, and an EL display devicehaving high reliability and which is capable of good image display (highoperation performance) can thus be formed.

[0107] Note that the most important point in the pixel structure of FIG.1 is that a multi-gate structure TFT is used as the switching TFT, andthat it is not necessary to place limits on the structure of FIG. 1 withregard to such things as the placement of LDD regions.

[0108] A more detailed explanation of the present invention, having theabove constitution, is now performed by the embodiments shown below.

[0109] Embodiment 1

[0110] The embodiments of the present invention are explained usingFIGS. 3A to 5C. A method of manufacturing a pixel portion, and TFTs of adriver circuit portion formed in the periphery of the pixel portion, isexplained here. Note that in order to simplify the explanation, a CMOScircuit is shown as a basic circuit for the driver circuits.

[0111] First, as shown in FIG. 3A, a base film 301 is formed with a 300nm thickness on a glass substrate 300. Silicon oxynitride films arelaminated as the base film 301 in embodiment 1. It is good to set thenitrogen concentration to between 10 and 25 wt % in the film contactingthe glass substrate 300.

[0112] Further, it is effective to form an insulating film, made fromthe same material as that of the first passivation film 41 shown in FIG.1, as a portion of the base film 301. A large electric current flows ina current control TFT, heat is easily generated, and therefore it iseffective to form the heat radiating layer as close as possible to thecurrent control TFT.

[0113] Next, an amorphous silicon film (not shown in the figures) isformed with a thickness of 50 nm on the base film 301 by a knowndeposition method. Note that it is not necessary to limit this to theamorphous silicon film, and another film may be formed provided that itis a semiconductor film containing an amorphous structure (including amicrocrystalline semiconductor film). In addition, a compoundsemiconductor film containing an amorphous structure, such as anamorphous silicon germanium film, may also be used. Further, the filmthickness may be made from 20 to 100 nm.

[0114] The amorphous silicon film is then crystallized by a knownmethod, forming a crystalline silicon film (also referred to as apolycrystalline silicon film or a polysilicon film) 302. Thermalcrystallization using an electric furnace, laser annealingcrystallization using a laser, and lamp annealing crystallization usingan infrared lamp exist as known crystallization methods. Crystallizationis performed in embodiment 1 using light from an excimer laser whichuses XeCl gas.

[0115] Note that pulse emission type excimer laser light formed into alinear shape is used in embodiment 1, but a rectangular shape may alsobe used, and continuous emission argon laser light and continuousemission excimer laser light can also be used.

[0116] The crystalline silicon film is used as an active layer of theTFTs in embodiment 1, but it is also possible to use an amorphoussilicon film as the active layer. However, it is necessary for a largecurrent to flow through the current control TFT, and therefore it ismore effective to use the crystalline silicon film, through whichcurrent easily flows.

[0117] Note that it is effective to form the active layer of theswitching TFT, in which there is a necessity to reduce the off current,by the amorphous silicon film, and to form the active layer of thecurrent control TFT by the crystalline silicon film. Electric currentflows with difficulty in the amorphous silicon film because the carriermobility is low, and the off current does not easily flow. In otherwords, the most can be made of the advantages of both the amorphoussilicon film, through which current does not flow easily, and thecrystalline silicon film, through which current easily flows.

[0118] Next, as shown in FIG. 3B, a protecting film 303 is formed on thecrystalline silicon film 302 from a silicon oxide film having athickness of 130 nm. This thickness may be chosen within the range of100 to 200 nm (preferably between 130 and 170 nm). Furthermore, otherfilms may also be used providing that they are insulating filmscontaining silicon. The protecting film 303 is formed so that thecrystalline silicon film is not directly exposed to plasma duringaddition of an impurity, and so that it is possible to have delicateconcentration control of the impurity.

[0119] Resist masks 304 a and 304 b are then formed on the protectingfilm 303, and an impurity element which imparts n-type conductivity(hereafter referred to as an n-type impurity element) is added. Notethat elements residing in periodic table group 15 are generally used asthe n-type impurity element, and typically phosphorous or arsenic can beused. Note that a plasma doping method is used, in which phosphine (PH₃)is plasma activated without separation of mass, and phosphorous is addedat a concentration of 1×10¹⁸ atoms/cm³ in embodiment 1. An ionimplantation method, in which separation of mass is performed, may alsobe used, of course.

[0120] The dose amount is regulated so that the n-type impurity elementis contained in n-type impurity regions 305 and 306, thus formed by thisprocess, at a concentration of 2×10¹⁶ to 5×10¹⁹ atoms/cm³ (typicallybetween 5×10¹⁷ and 5×10¹⁸ atoms/cm³).

[0121] Next, as shown in FIG. 3C, the protecting film 303 is removed,and activation of the added periodic table group 15 element isperformed. A known technique of activation may be used as the means ofactivation, and activation is done in embodiment 1 by irradiation ofexcimer laser light. Both of pulse emission type laser and a continuousemission type laser may be used, and it is not necessary to place anylimits on the use of excimer laser light. The goal is the activation ofthe added impurity element, and it is preferable that irradiation isperformed at an energy level at which the crystalline silicon film doesnot melt. Note that the laser irradiation may also be performed with theprotecting film 303 in place.

[0122] Activation by heat treatment may also be performed along withactivation of the impurity element by laser light. When activation isperformed by heat treatment, considering the heat resistance of thesubstrate, it is good to perform heat treatment on the order of 450 to550° C.

[0123] A boundary portion (connecting portion) with regions along theedges of the n-type impurity regions 305 and 306, namely regions alongthe perimeter into which the n-type impurity element, which exists inthe n-type impurity regions 305 and 306, is not added, is defined bythis process. This means that, at the point when the TFTs are latercompleted, extremely good connections can be formed between LDD regionsand channel forming regions.

[0124] Unnecessary portions of the crystalline silicon film are removednext, as shown in FIG. 3D, and island shape semiconductor films(hereafter referred to as active layers) 307 to 310 are formed.

[0125] Then, as shown in FIG. 3E, a gate insulating film 311 is formed,covering the active layers 307 to 310. An insulating film containingsilicon and with a thickness of 10 to 200 nm, preferably between 50 and150 nm, may be used as the gate insulating film 311. A single layerstructure or a lamination structure may be used. A 110 nm thick siliconoxynitride film is used in embodiment 1.

[0126] A conducting film with a thickness of 200 to 400 nm is formednext and patterned, forming gate electrodes 312 to 316. Note that inembodiment 1, the gate electrodes and lead wirings electricallyconnected to the gate electrodes (hereafter referred to as gate wirings)are formed from different materials. Specifically, a material having alower resistance than that of the gate electrodes is used for the gatewirings. This is because a material which is capable of beingmicro-processed is used as the gate electrodes, and even if the gatewirings cannot be micro-processed, the material used for the wirings haslow resistance. Of course, the gate electrodes and the gate wirings mayalso be formed from the same material.

[0127] Further, the gate wirings may be formed by a single layerconducting film, and when necessary, it is preferable to use a two layeror a three layer lamination film. All known conducting films can be usedas the gate electrode material. However, as stated above, it ispreferable to use a material which is capable of being micro-processed,specifically, a material which is capable of being patterned to a linewidth of 2 μm or less.

[0128] Typically, a film of a material chosen from among the groupconsisting of tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), and chromium (Cr); or a nitrated compound of the above elements(typically a tantalum nitride film, a tungsten nitride film, or atitanium nitride film); or an alloy film of a combination of the aboveelements (typically a Mo—W alloy or a Mo—Ta alloy); or a silicide filmof the above elements (typically a tungsten silicide film or a titaniumsilicide film); or a silicon film which has been made to possessconductivity can be used. A single layer film or a lamination may beused, of course.

[0129] A lamination film made from a 50 nm thick tantalum nitride (TaN)film and a 350 nm thick Ta film is used in embodiment 1. It is good toform this film by sputtering. Furthermore, if an inert gas such as Xe orNe is added as a sputtering gas, then film peeling due to the stress canbe prevented.

[0130] The gate electrodes 313 and 316 are formed at this time so as tooverlap a portion of the n-type impurity regions 305 and 306,respectively, sandwiching the gate insulating film 311. This overlappingportion later becomes an LDD region overlapping the gate electrode.

[0131] Next, an n-type impurity element (phosphorous is used inembodiment 1) is added in a self-aligning manner with the gateelectrodes 312 to 316 as masks, as shown in FIG. 4A. The addition isregulated so that phosphorous is added to impurity regions 317 to 323thus formed at a concentration of {fraction (1/10)} to ½ that of theimpurity regions 305 and 306 (typically between ¼ and ⅓). Specifically,a concentration of 1×10¹⁶ to 5×10¹⁸ atoms/cm³ (typically 3×10¹⁷ to3×10¹⁸ atoms/cm³) is preferable.

[0132] Resist masks 324 a to 324 d are formed next to cover the gateelectrodes, as shown in FIG. 4B, and an n-type impurity element(phosphorous is used in embodiment 1) is added, forming impurity regions325 to 331 containing a high concentration of phosphorous. Ion dopingusing phosphine (PH₃) is also performed here, and is regulated so thatthe phosphorous concentration of these regions is from 1×10²⁰ to 1×10²¹atoms/cm³ (typically between 2×10²⁰ and 5×10²⁰ atoms/cm³).

[0133] A source region or a drain region of the n-channel TFT is formedby this process, and in the switching TFT, a portion of the n-typeimpurity regions 320 to 322 formed by the process of FIG. 4A remains.These remaining regions correspond to the LDD regions 15 a to 15 d ofthe switching TFT in FIG. 1.

[0134] Next, as shown in FIG. 4C, the resist masks 324 a to 324 d areremoved, and a new resist mask 332 is formed. A p-type impurity element(boron is used in embodiment 1) is then added, forming impurity regions333 and 334 containing a high concentration of boron. Boron is addedhere to a concentration of 3×10²⁰ to 3×10²¹ atoms/cm³ (typically between5×10²⁰ and 1×10²¹ atoms/cm³) by ion doping using diborane (B₂H₆).

[0135] Note that phosphorous has already been added to the impurityregions 333 and 334 at a concentration of 1×10¹⁶ to 5×10¹⁸ atoms/cm³,but boron is added here at a concentration of at least 3 times that ofthe phosphorous. Therefore, the n-type impurity regions already formedcompletely invert to p-type, and function as p-type impurity regions.

[0136] Next, after removing the resist mask 332, the n-type and p-typeimpurity elements added at various concentrations are activated. Furnaceannealing, laser annealing, or lamp annealing may be performed as ameans of activation. Heat treatment is performed in embodiment 1 in anitrogen atmosphere for 4 hours at 550° C. in an electric furnace.

[0137] It is important to remove as much of the oxygen in the atmosphereas possible at this time. This is because if any oxygen exists, then theexposed surface of the electrode oxidizes, inviting an increase inresistance, and at the same time it becomes more difficult to later makean ohmic contact. It is therefore preferable that the concentration ofoxygen in the atmosphere in the above activation process be 1 ppm orless, desirably 0.1 ppm or less.

[0138] After the activation process is completed, a gate wiring 335 witha thickness of 300 nm is formed next. A metallic film having aluminum(Al) or copper (Cu) as its principal constituent (comprising 50 to 100%of the composition) may be used as the material of the gate wiring 335.As with the gate wiring 211 of FIG. 2, the gate wiring 335 is formedwith a placement so that the gate electrodes 314 and 315 of theswitching TFTs (corresponding to gate electrodes 19 a and 19 b of FIG.2) are electrically connected. (See FIG. 4D.)

[0139] The wiring resistance of the gate wiring can be made extremelysmall by using this type of structure, and therefore a pixel displayregion (pixel portion) having a large surface area can be formed.Namely, the pixel structure of embodiment 1 is extremely effectivebecause an EL display device having a screen size of a 10 inch diagonalor larger (in addition, a 30 inch or larger diagonal) is realized.

[0140] A first interlayer insulating film 336 is formed next, as shownin FIG. 5A. A single layer insulating film containing silicon is used asthe first interlayer insulating film 336, but a lamination film may becombined in between. Further, a film thickness of between 400 nm and 1.5μm may be used. A lamination structure of an 800 nm thick silicon oxidefilm on a 200 nm thick silicon oxynitride film is used in embodiment 1.

[0141] In addition, heat treatment is performed for 1 to 12 hours at 300to 450° C. in an atmosphere containing between 3 and 100% hydrogen,performing hydrogenation. This process is one of hydrogen termination ofdangling bonds in the semiconductor film by hydrogen which is thermallyactivated. Plasma hydrogenation (using hydrogen activated by a plasma)may also be performed as another means of hydrogenation.

[0142] Note that the hydrogenation step may also be inserted during theformation of the first interlayer insulating film 336. Namely, hydrogenprocessing may be performed as above after forming the 200 nm thicksilicon oxynitride film, and then the remaining 800 nm thick siliconoxide film may be formed.

[0143] A contact hole is formed next in the first interlayer insulatingfilm 336, and source wirings 337 to 340, and drain wirings 341 to 343are formed. In embodiment 1, a lamination film with a three layerstructure of a 100 nm titanium film, a 300 nm aluminum film containingtitanium, and a 150 nm titanium film, formed successively by sputtering,is used as these wirings. Other conducting films may also be used, ofcourse, and an alloy film containing silver, palladium, and copper mayalso be used.

[0144] A first passivation film 344 is formed next with a thickness of50 to 500 nm (typically between 200 and 300 nm). A 300 nm thick siliconoxynitride film is used as the first passivation film 344 inembodiment 1. This may also be substituted by a silicon nitride film. Itis of course possible to use the same materials as those of the firstpassivation film 41 of FIG. 1.

[0145] Note that it is effective to perform plasma processing using agas containing hydrogen such as H₂ or NH₃ before the formation of thesilicon oxynitride film. Hydrogen activated by this preprocess issupplied to the first interlayer insulating film 336, and the filmquality of the first passivation film 344 is improved by performing heattreatment. At the same time, the hydrogen added to the first interlayerinsulating film 336 diffuses to the lower side, and the active layerscan be hydrogenated effectively.

[0146] Next, as shown in FIG. 5B, a color filter 345 and a fluorescingbody 346 are formed. Known materials may be used for these. Furthermore,they may be formed by being patterned separately, or they may be formedin succession and then patterned together. A method such as screenprinting, ink jetting, or mask evaporation (a selective forming methodusing a mask material) may be used as the formation method.

[0147] The respective film thickness may be chosen in the range of 0.5to 5 μm (typically between 1 and 2 μm). In particular, the optimal filmthickness of the fluorescing body 346 varies with the material used. Inother words, if it is too thin, then the color transformation efficiencybecomes poor, and if it is too thick, then the step becomes large andthe amount of light transmitted drops. Optimal film thicknesses musttherefore be set by taking a balance of both characteristics.

[0148] Note that, in embodiment 1, an example of a color changing methodin which the light emitted from the EL layer is transformed in color,but if a method of manufacturing individual EL layers which correspondto R, G, and B, is employed, then the color filter and the fluorescingbody can be omitted.

[0149] A second interlayer insulating film 347 is formed next from aresin. Materials such as polyimide, polyamide, acrylic, and BCB(benzocyclobutene) can be used as the resin. In particular, the purposeof being a leveling film is strong in the second interlayer insulatingfilm 347, and therefore acrylic, having superior levelingcharacteristics, is preferable. An acrylic film is formed in embodiment1 with a film thickness which can sufficiently level the step betweenthe color filter 345 and the fluorescing body 346. This thickness ispreferably from 1 to 5 μm (more preferably between 2 and 4 μm).

[0150] A second passivation film 348 is then formed on the secondinterlayer insulating film 347 to 100 nm thickness. An insulating filmcomprising Si, Al, N, O and La is used in the present embodiment. Acontact hole for reaching the drain wiring 343 is then formed. in thesecond passivation film 348, in the second interlayer insulating film347 and in the first passivation film 344, and a pixel electrode 349 isformed. A compound of indium oxide and tin oxide is formed into 110 nmthick in embodiment 1, and patterning is performed, making the pixelelectrode. The pixel electrode 349 becomes an anode of the EL element.Note that it is also possible to use other materials: a compound film ofindium oxide and zinc oxide, or a zinc oxide film containing galliumoxide.

[0151] Note that embodiment 1 becomes a structure in which the pixelelectrode 349 is electrically connected to the drain region 331. of thecurrent control TFT, through the drain wiring 343. This structure hasthe following advantages.

[0152] The pixel electrode 349 becomes directly connected to an organicmaterial such as the EL layer (emitting layer) or a charge transportinglayer, and therefore it is possible for the mobile ions contained in theEL layer to diffuse throughout the pixel electrode. In other words,without connecting the pixel electrode 348 directly to the drain region331, a portion of the active layer, the introduction of mobile ions intothe active layer due to the drain wiring 343 being interrupted can beprevented in the structure of embodiment 1.

[0153] Next, as shown in FIG. 5C, an EL layer 350, a cathode (MgAgelectrode) 351, and a protecting electrode 352 are formed in successionwithout exposure to the atmosphere. It is preferable, at this point, toperform heat treatment of the pixel electrode 349, completely removingall moisture, before forming the EL layer 350 and the cathode 351. Notethat a known material can be used as the EL layer 350.

[0154] The materials explained in the “embodiment mode” section of thisspecification can be used as the EL layer 350. In embodiment 1, an ELlayer having a 4 layer structure of a hole injecting layer, a holetransporting layer, an emitting layer, and an electron transportinglayer is used, as shown in FIG. 19, but there are cases in which theelectron transporting layer is not formed, and cases in which anelectron injecting layer is also formed. Furthermore, there are alsocases in which the hole injecting layer is omitted. Several examples ofthese types of combinations have already been reported, and any of theseconstitutions may be used.

[0155] An amine such as TPD (triphenylamine dielectric) may be used asthe hole injecting layer or as the hole transporting layer, and inaddition, a hydrazone (typically DEH), a stilbene (typically STB), or astarburst (typically m-MTDATA) can also be used. In particular, astarburst material, which has a high glass transition temperature and isdifficult to crystallize, is preferable. Further, polyaniline (PAni),polythiophene (PEDOT), and copper phthalocyanine (CuPc) may also beused.

[0156] BPPC, perylene, and DCM can be used as a red color emitting layerin the emitting layer, and in particular, the Eu complex shown byEu(DBM)₃(Phen) (refer to Kido, J., et. al, Appl. Phys., vol. 35, pp.L394-6, 1996 for details) is highly monochromatic, possessing a sharpemission at a wavelength of 620 nm.

[0157] Further, typically an Alq₃ (8-hydroxyquinoline aluminum) materialin which quinacridone or coumarin is added at a level of several mol %can be used as a green color emitting layer. The chemical formula is asshown below.

[0158] In addition, typically a distile-arylene amino dielectric, inwhich amino substituted DSA is added to DSA (distile-arylene dielectric)can be used as a blue color emitting layer. In particular, it ispreferable to use the high performance materialdistilyl-biphenyl(DPVBi). Its chemical formula is as shown below.

[0159] Though it is possible to protect the EL layer 350 from moistureand oxygen with the protecting electrode 352, more preferably a thirdpassivation film 353 may be formed. In the present embodiment a 300 nmthick silicon oxynitride film is disposed as the third passivation film353. It is acceptable to successively form the third passivation filmafter the protecting electrode 352 without exposure to the atmosphere.The same materials as those of the third passivation film 50 of FIG. 1can also be used, of course, as the third passivation film 353.

[0160] A 4 layer structure made from a hole injecting layer, a holetransporting layer, an emitting layer, and an electron injecting layeris used in embodiment 1, but there are already examples of manycombinations already reported, and any of these constitutions may alsobe used. Furthermore, an MgAg electrode is used as the cathode of the ELelement in embodiment 1, but other known materials may also be used.

[0161] The protecting electrode 352 is formed in order to preventdeterioration of the MgAg electrode 351, and a metallic film havingaluminum as its principal constituent is typical. Other materials may,of course, also be used. Furthermore, the EL layer 350 and the MgAgelectrode 351 are extremely weak with respect to moisture, and thereforeit is preferable to perform successive formation up through to theprotecting electrode 352 without exposure to the atmosphere, protectingthe EL layer from external air.

[0162] Note that the film thickness of the EL layer 350 may be from 10to 400 nm (typically between 60 and 160 nm), and that the thickness ofthe MgAg electrode 351 may be from 180 to 300 nm (typically between 200and 250 nm).

[0163] The active matrix type EL display device with the structure shownin FIG. 5C is thus completed. By arranging TFTs with optimal structurein not only the pixel portion, but also in the driver circuit portion,the active matrix type EL display device of embodiment 1 shows extremelyhigh reliability, and the operational characteristics can be raised.

[0164] First, a TFT having a structure which reduces hot carrierinjection as much as possible without a drop in the operation speed isused as an n-channel TFT 205 of the CMOS circuit forming the drivercircuits. Note that the driver circuits referred to here includecircuits such as a shift register, a buffer, a level shifter, and asampling circuit (also referred to as a transfer gate). When digitaldriving is performed, signal conversion circuits such as a D/A convertercircuit are also included.

[0165] In the case of embodiment 1, an active layer of the n-channel TFT205 includes a source region 355, a drain region 356, an LDD region 357,and a channel forming region 358, as shown in FIG. 5C, and the LDDregion 357 overlaps the gate electrode 313, sandwiching the gateinsulating film 311.

[0166] The formation of the LDD region on the drain side only is inconsideration of not lowering the operation speed. Further, it is notnecessary to be concerned with the value of the off current in then-channel TFT 205, and greater emphasis may be placed on the operationspeed. It is therefore preferable that the LDD region 357 completelyoverlap the gate electrode 313, reducing resistive components as much aspossible. In other words, it is good to eliminate all offset.

[0167] Deterioration of a p-channel TFT 206 of the CMOS circuit due tohot carrier injection is almost of no concern, and in particular,therefore, an LDD region is not formed. It is also possible, of course,to take action against hot carriers by forming an LDD region similar tothat of the n-channel TFT 205.

[0168] Note that among the driver circuits, the sampling circuit issomewhat special when compared to the other circuits, and a largecurrent flows in the channel forming region in both directions. Namely,the roles of the source region and the drain region change. In addition,it is necessary to suppress the value of the off current as much aspossible, and with that in mind, it is preferable to arrange a TFThaving functions at an intermediate level between the switching TFT andthe current control TFT.

[0169] It is preferable, therefore, to arrange a TFT with the structureshown in FIG. 9 as an n-type TFT forming the sampling circuit. As shownin FIG. 9, a portion of LDD regions 901 a and 901 b overlap a gateelectrode 903, sandwiching a gate insulating film 902. This effect is asstated in the explanation of the current control TFT 202, and the caseof the sampling circuit differs in the point of forming the LDD regions901 a and 901 b with a shape that sandwiches a channel forming region904.

[0170] Further, a pixel with the structure shown in FIG. 1 is formed,forming a pixel portion. The structures of a switching TFT and a currentcontrol TFT formed within the pixel have already been explained in FIG.1, and therefore that explanation is omitted here.

[0171] Note that, in practice, it is preferable to additionally performpackaging (sealing) after completing up through FIG. 5C by using ahousing material such as a highly airtight protecting film (such as alaminar film or an ultraviolet hardened resin film) or a ceramic sealingcan, so that there is no exposure to the atmosphere. By making theinside of the housing material an inert environment, and by placing anabsorbing agent (for example, barium oxide) within the housing material,the reliability (life) of the EL layer is increased.

[0172] Furthermore, after the airtightness is increased by the packagingprocessing, a connector (a flexible printed circuit, FPC) for connectingbetween output terminals from elements or circuits formed on thesubstrate, and external signal terminals, is attached, completing amanufactured product. The EL display device in this state of being ableto be shipped is referred to as an EL module throughout thisspecification.

[0173] The constitution of the active matrix type EL display device ofembodiment 1 is explained here using the perspective view of FIG. 6. Theactive matrix type EL display device of embodiment 1 is formed on aglass substrate 601, and is composed of a pixel portion 602, a gate sidedriving circuit 603, and a source side driving circuit 604. A switchingTFT 605 of the pixel portion is an n-channel TFT, and is placed at theintersection of a gate wiring 606 connected to the gate side drivingcircuit 603, and a source wiring 607 of the source side driving circuit604. Furthermore, the drain of the switching TFT 605 is electricallyconnected to the gate of a current control TFT 608.

[0174] In addition, the source of the current control TFT 608 isconnected to a current supply line 609, and an EL element 610 iselectrically connected to the drain of the current control TFT 608.Provided that the current control TFT 608 is an n-channel TFT, it ispreferable to connect the cathode of the EL element 610 to the drain ofthe current control TFT 608 at this point. Further, if the currentcontrol TFT 608 is a p-channel TFT, then it is preferable to connect theanode of the EL element 610 to the drain of the current control TFT 608.

[0175] Input wirings (connection wirings) 612 and 613, and an inputwiring 614 which is connected to the current supply line 609, are thenformed in an external input terminal FPC 611 in order to transfersignals to the driver circuits.

[0176] Shown in FIG. 7 is one example of the circuit composition of theEL display device shown in FIG. 6. The EL display device of embodiment 1has a source side driving circuit 701, a gate side driving circuit (A)707, a gate side driving circuit (B) 711, and a pixel portion 706. Notethat, throughout this specification, driver circuit is a generic termwhich includes source side driver circuits and gate side drivercircuits.

[0177] The source side driving circuit 701 is provided with a shiftregister 702, a level shifter 703, a buffer 704, and a sampling circuit(transfer gate) 705. In addition, the gate side driving circuit (A) 707is provided with a shift register 708, a level shifter 709, and a buffer710. The gate side driving circuit (B) 711 has a similar composition.

[0178] The driving voltage is from 5 to 16 V (typically 10 V) for theshifter registers 702 and 708 here, and the structure shown by referencenumeral 205 of FIG. 5C is suitable for an n-channel TFT used in a CMOScircuit forming the circuits.

[0179] Furthermore, the driving voltage becomes high at between 14 and16 V for the level shifters 703 and 709, and for the buffers 704 and710, and similar to the shifters, a CMOS circuit containing then-channel TFT 205 of FIG. 5C is suitable. Note that the use of amulti-gate structure, such as a double gate structure or a triple gatestructure for the gate wirings, is effective by increasing thereliability of each circuit.

[0180] The driving voltage is between 14 and 16 V for the samplingcircuit 705, but it is necessary to reduce the value of the off currentbecause the source region and the drain region invert, and therefore aCMOS circuit containing the n-channel TFT 208 of FIG. 9 is suitable.

[0181] In addition, the driving voltage of the pixel portion 706 isbetween 14 and 16 V, and a pixel with the structure shown in FIG. 1 isarranged.

[0182] Note that the above constitutions can be easily realized bymanufacturing TFTs in accordance with the manufacturing processes shownin FIGS. 3A to 5C. Furthermore, only the constitution of the pixelportion and the driver circuits is shown in embodiment 1, but it is alsopossible to form other logic circuits, in addition to the drivingcircuits, on the same substrate and in accordance with the manufacturingprocess of embodiment 1, such as a signal divider circuit, a D/Aconverter circuit, an op-amp circuit, and a γ compensation circuit. Inaddition, it is considered that circuits such as a memory portion and amicroprocessor can also be formed.

[0183] An explanation of the EL module of embodiment 1, containing thehousing material, is made using FIGS. 17A and 17B. Note that, whennecessary, the symbols used in FIGS. 6 and 7 are cited.

[0184] A pixel portion 1701, a source side driving circuit 1702, and agate side driving circuit 1703 are formed on a substrate (including abase film underneath a TFT) 1700. Various wirings from the respectivedriver circuits are connected to external equipment, via the FPC 611,through the input wirings 612 to 614.

[0185] A housing material 1704 is formed at this point enclosing atleast the pixel portion, and preferably the driving circuits and thepixel portion. Note that the housing material 1704 is of an irregularshape in which the internal size is larger than the external size of theEL element, or has a sheet shape, and is fixed to the substrate 1700 byan adhesive 1705 so as to form an airtight space jointly with thesubstrate 1700. At this point, the EL element is in a state of beingcompletely sealed in the above airtight space, and is completely cutofffrom the external atmosphere. Note that a multiple number of housingmaterials 1704 may be formed.

[0186] It is preferable to use an insulating substance such as a glassor a polymer as the housing material 1704. The following can be given asexamples: amorphous glass (such as borosilicate glass or quartz);crystallized glass; ceramic glass; organic resins (such as acrylicresins, styrene resins, polycarbonate resins, and epoxy resins); andsilicone resins. In addition, ceramics may also be used. Furthermore,provided that the adhesive 1705 is an insulating material, it is alsopossible to use a metallic material such as a stainless alloy.

[0187] It is possible to use an adhesive such as an epoxy resin or anacrylate resin as the material of the adhesive 1705. In addition, athermally hardened resin or a light hardened resin can also be used asthe adhesive. Note that it is necessary to use a material through which,as much as is possible, oxygen and moisture is not transmitted.

[0188] In addition, it is preferable to fill an opening 1706 between thehousing material and the substrate 1700 with an inert gas (such asargon, helium, or nitrogen). There are no limitations on a gas, and itis also possible to use an inert liquid (such as a liquid fluorinatedcarbon, typically perfluoroalkane). The materials such as those used byJapanese Patent Application Laid-open No. Hei 8-78519 may be referred toregarding inert liquids. The space may also be filled with a resin.

[0189] It is effective to form drying agent in the opening 1706.Materials such as those recorded in Japanese Patent ApplicationLaid-open No. Hei 9-148066 can be used as the drying agent. Typically,barium oxide may be used. Furthermore, it is effective to form anantioxidizing agent as well, not just a drying agent.

[0190] A plural number of isolated pixels having EL elements are formedin the pixel portion, as shown in FIG. 17B, and all of the pixels have aprotecting electrode 1707 as a common electrode. In embodiment 1 it ispreferable to form the EL layer, the cathode (MgAg electrode), and theprotecting electrode in succession, without exposure to the atmosphere.The EL layer and the cathode are formed using the same mask material,and provided that only the protecting electrode is formed by a separatemask material, then the structure of FIG. 17B can be realized.

[0191] The EL layer and the cathode may be formed only in the pixelportion at this point, and it is not necessary to form them on thedriving circuits. There is no problem, of course, with forming them onthe driving circuits, but considering the fact that alkaline metals arecontained in the EL layer, it is preferable to not form it over thedriving circuits.

[0192] Note that an input wiring 1709 is connected to the protectingelectrode 1707 in a region shown by reference numeral 1708. The inputwiring 1709 is a wiring for providing a preset voltage to the protectingelectrode 1707, and is connected to the FPC 611 through a conductingpaste material (typically an anisotropic conducting film) 1710.

[0193] A manufacturing process for realizing a contact structure in theregion 1708 is explained here using FIGS. 18A to 18C.

[0194] First, the state of FIG. 5A is obtained in accordance with theprocesses of embodiment 1. At this point the first interlayer insulatingfilm 336 and the gate insulating film 311 are removed from the edges ofthe substrate (in the region shown by reference numeral 1708 in FIG.17B), and the input wiring 1709 is formed on that region. The sourcewirings and the drain wirings of FIG. 5A are of course formed at thesame time. (See FIG. 18A.)

[0195] Next, when etching the second passivation film 348, the secondinterlayer insulating film 347 and the first passivation film 344 inFIG. 5B, a region shown by reference numeral 1801 is removed, and anopen portion 1802 is formed. (See FIG. 18B.)

[0196] The processes of forming the EL element (pixel electrode, ELlayer, and cathode formation processes) in the pixel portion areperformed in this state. A mask material is used in the region shown inFIGS. 18A to 18C at this time so that the EL element is not formed inthis region. After forming the cathode 351, the protecting electrode 352is formed using a separate mask material. The protecting electrode 352and the input wiring 1709 are thus electrically connected. Further, thethird passivation film 353 is formed, and the state of FIG. 18C isobtained.

[0197] The contact structure of the region shown by reference numeral1708 in FIG. 17B is thus realized by the above steps. The input wiring1709 is then connected to the FPC 611 through the opening between thehousing material 1704 and the substrate 1700 (note that this is filledby the adhesive 1705; in other words, it is necessary for the thicknessof the adhesive 1705 to be such that it can sufficiently level the stepof the input wiring). Note that an explanation of the input wiring 1709is made here, but the other input wirings 612 to 614 are also similarlyconnected to the FPC 611 by passing under the housing material 1704.

[0198] Embodiment 2

[0199] In embodiment 2, an example of a pixel constitution is shown inFIG. 10 which differs from the constitution shown in FIG. 2B.

[0200] The two pixels shown in FIG. 2B are arranged with symmetry aroundthe current supply line in embodiment 2. Namely, as shown in FIG. 10, bymaking the current supply line 213 common between the two pixelsneighboring the current supply line, the number of wirings needed can bereduced. Note that the structure of the TFTs placed inside the pixelsmay be left as is.

[0201] If this type of constitution is used, then it becomes possible tomanufacture a very high precision pixel portion, increasing the imagequality.

[0202] Note that the constitution of embodiment 2 can easily be realizedin accordance with the manufacturing processes of embodiment 1, and thatthe explanations of embodiment 1 and of FIG. 1 may be referencedregarding points such as the structure of the TFTs.

[0203] Embodiment 3

[0204] A case of forming a pixel portion having a structure whichdiffers from that of FIG. 1 is explained using FIG. 11 in embodiment 3.Note that processes up through the formation of the second interlayerinsulating film 44 may be performed in accordance with embodiment 1.Furthermore, the structures of the switching TFT 201 and the currentcontrol TFT 202, covered by the second interlayer insulating film 44,are the same as those of FIG. 1, and their explanation here is omitted.

[0205] In the case of embodiment 3, a pixel electrode 51, a cathode 52,and an EL layer 53 are formed after forming a contact hole in the secondpassivation film 45, the second interlayer insulating film 44 and thefirst passivation film 41. The cathode 52 and the EL layer 53 are formedin succession, without exposure to the atmosphere, by vacuum evaporationin embodiment 3, and at that time a red color emitting EL layer, a greencolor emitting EL layer, and a blue color emitting layer are formedselectively in separate pixels by using a mask material. Note that whileonly one pixel is shown in FIG. 11, pixels with the same structure areformed corresponding to the colors of red, green, and blue,respectively, and that color display can be performed by these pixels. Aknown material may be employed for each EL layer color.

[0206] A 150 nm thick aluminum alloy film (an aluminum film containing 1wt % of titanium) is formed as the pixel electrode 51 in embodiment 3.Provided that it is a metallic material, any material may be used as thepixel electrode material, but it is preferable to use a material havinga high reflectivity. Further, a 230 nm thick MgAg electrode is used asthe cathode 52, and the film thickness of the EL layer 53 is 120 nm.

[0207] An anode 54 made from a transparent conducting film (an ITO filmin embodiment 3) is formed next with a thickness of 110 nm. An ELelement 209 is thus formed, and if a third passivation film 55 is formedby the same materials as shown in embodiment 1, then a pixel with thestructure shown in FIG. 11 is completed.

[0208] When using the structure of embodiment 3, the red, green, or bluelight generated by each pixel is irradiated in the opposite direction asthat of the substrate on which the TFTs are formed. For that reason,almost the entire area inside the pixel, namely the region in which theTFTs are formed, can be used as an effective emitting region. As aresult, there is a sharp increase in the effective emitting surface areaof the pixel, and the brightness and the contrast ratio (the ratiobetween light and dark) of the image are increased.

[0209] Note that it is possible to freely combine the composition ofembodiment 3 with the constitutions of any of embodiments 1 and 2.

[0210] Embodiment 4

[0211] A case of forming a pixel having a structure which differs fromthat of FIG. 2 of embodiment 1 is explained in embodiment 4 using FIGS.12A and 12B.

[0212] In FIG. 12A, reference numeral 1201 denotes a switching TFT,which comprises an active layer 56, a gate electrode 57 a, a gate wiring57 b, a source wiring 58, and a drain wiring 59. Further, referencenumeral 1202 denotes a current control TFT, which comprises an activelayer 60, a gate electrode 61, a source wiring (current supply line) 62,and a drain wiring 63 are included in its constitution. The sourcewiring 62 of the current control TFT 1202 is connected to a currentsupply line 64, and the drain wiring 63 is connected to an EL element65. FIG. 12B shows the circuit composition of this pixel.

[0213] The point of difference between FIG. 12A and FIG. 2A is thestructure of the switching TFT. In embodiment 4 the gate electrode 57 ais formed with a fine line width between 0.1 and 5 μm, and the activelayer 56 is formed so as to transverse that portion. The gate wiring 57b is formed so as to electrically connect the gate electrode 57 a ofeach pixel. A triple gate structure which does not monopolize muchsurface area is thus realized.

[0214] Other portions are similar to those of FIG. 2A, and the effectiveemitting surface area becomes larger because the surface areaexclusively used by the switching TFT becomes smaller if the structureof embodiment 4 is employed. In other words, the image brightness isincreased. Furthermore, a gate structure in which redundancy isincreased in order to reduce the value of the off current can berealized, and therefore the image quality can be increased even further.

[0215] Note that, in the constitution of embodiment 4, the currentsupply line 64 can be made common between neighboring pixels, as inembodiment 2, and that a structure like that of embodiment 3 may also beused. Furthermore, processes of manufacturing may be performed inaccordance with those of embodiment 1.

[0216] Embodiment 5

[0217] Cases in which a top gate type TFT is used are explained inembodiments 1 to 4, and the present invention may also be implementedusing a bottom gate type TFT. A case of implementing the presentinvention by using a reverse stagger type TFT is explained in embodiment5 using FIG. 13. Note that, except for the structure of the TFT, thestructure is the same as that of FIG. 1, and therefore the same symbolsas those of FIG. 1 are used when necessary.

[0218] In FIG. 13, the similar materials as those of FIG. 1 can be usedin the substrate 11 and in the base film 12. A switching TFT 1301 and acurrent control TFT 1302 are then formed on the base film 12.

[0219] The switching TFT 1301 comprises: gate electrodes 70 a and 70 b;a gate wiring 71; a gate insulating film 72; a source region 73; a drainregion 74; LDD regions 75 a to 75 d; a high concentration impurityregion 76; channel forming regions 77 a and 77 b; channel protectingfilms 78 a and 78 b; a first interlayer insulating film 79; a sourcewiring 80; and a drain wiring 81.

[0220] Further, the current control TFT 1302 comprises: a gate electrode82; the gate insulating film 72; a source region 83; a drain region 84;an LDD region 85; a channel forming region 86; a channel protecting film87; a first interlayer insulating film 79; a source wiring 88; and adrain wiring 89. The gate electrode 82 is electrically connected to thedrain wiring 81 of the switching TFT 1301 at this point.

[0221] Note that the above switching TFT 1301 and the current controlTFT 1302 may be formed in accordance with a known method ofmanufacturing a reverse stagger type TFT. Further, similar materialsused in corresponding portions of the top gate type TFTs of embodiment 1can be used for the materials of each portion (such as wirings,insulating films, and active layers) formed in the above TFTs. Note thatthe channel protecting films 78 a, 78 b, and 87, which are not in theconstitution of the top gate type TFT, may be formed by an insulatingfilm containing silicon. Furthermore, regarding the formation ofimpurity regions such as the source regions, the drain regions, and theLDD regions, they may be formed by using a photolithography techniqueand individually changing the impurity concentration.

[0222] When the TFTs are completed, a pixel having an EL element 1303 inwhich the first passivation film 41, the color filter 42, thefluorescent substance 43, the second interlayer insulating film(leveling film) 44, the second passivation film 45, the pixel electrode(anode) 46, the EL layer 47, the MgAg electrode (cathode) 48, thealuminum electrode (protecting film) 49, and the third passivation film50 are formed in order, is completed. Embodiment 1 may be referred towith respect to manufacturing processes and materials for the above.

[0223] Note that it is possible to freely combine the constitution ofembodiment 5 with the constitution of any of embodiments 2 to 4.

[0224] Embodiment 6

[0225] It is effective to use a material having a high thermal radiatingeffect, similar to that of the second passivation film 45, as the basefilm formed between the active layer and the substrate in the structuresof FIG. 5C of embodiment 1 or FIG. 1. In particular, a large amount ofcurrent flows in the current control TFT, and therefore heat is easilygenerated, and deterioration due to self generation of heat can become aproblem. Thermal deterioration of the TFT can be prevented by using thebase film of embodiment 6, which has a thermal radiating effect, forthis type of case.

[0226] The effect of protecting from the diffusion of mobile ions fromthe substrate is also very important, of course, and therefore it ispreferable to use a lamination structure of a compound including Si, Al,N, O, and M, and an insulating film containing silicon, similar to thefirst passivation film 41.

[0227] Note that it is possible to freely combine the constitution ofembodiment 6 with the constitution of any of embodiments 1 to 5.

[0228] Embodiment 7

[0229] When the pixel structure shown in embodiment 3 is used, the lightemitted from the EL layer is radiated in the direction opposite to thesubstrate, and therefore it is not necessary to pay attention to thetransmissivity of materials, such as the insulating film, which existbetween the substrate and the pixel electrode. In other words, materialswhich have a somewhat low transmissivity can also be used.

[0230] It is therefore advantageous to use a carbon film, such as onereferred to as a diamond thin film, a diamond-like carbon film, or anamorphous carbon film, as the base film 12, the first passivation film41 or the second passivation film 45. In other words, because it is notnecessary to worry about lowering the transmissivity, the film thicknesscan be set thick, to between 100 and 500 nm, and it is possible to havea very high thermal radiating effect.

[0231] Regarding the use of the above carbon films in the thirdpassivation film 50, note that a reduction in the transmissivity must beavoided, and therefore it is preferable to set the film thickness tobetween 5 and 100 nm.

[0232] Note that, in embodiment 7, it is effective to laminate withanother insulating film when a carbon film is used in any of the basefilm 12, the first passivation film 41, the second passivation film 45,or the third passivation film 50.

[0233] In addition, embodiment 7 is effective when the pixel structureshown in embodiment 3 is used, and for other constitutions, it ispossible to freely combine the constitution of embodiment 7 with theconstitution of any of embodiments 1 to 6.

[0234] Embodiment 8

[0235] The amount of the off current value in the switching TFT in thepixel of the EL display device is reduced by using a multi-gatestructure for the switching TFT, and the present invention ischaracterized by the elimination of the need for a storage capacitor.This is a device for making good use of the surface area, reserved forthe storage capacitor, as an emitting region.

[0236] However, even if the storage capacitor is not completelyeliminated, an effect of increasing the effective emitting surface area,by the amount that the exclusive surface area is made smaller, can beobtained. In other words, the object of the present invention can besufficiently achieved by reducing the value of the off current by usinga multi-gate structure for the switching TFT, and by only shrinking theexclusive surface area of the storage capacitor.

[0237] It is therefore possible to use a pixel structure such as thatshown in FIG. 14. Note that, when necessary, the same symbols are usedin FIG. 14 as in FIG. 1.

[0238] The different point between FIG. 14 and FIG. 1 is the existenceof a storage capacitor 1401 connected to the switching TFT. The storagecapacitor 1401 is formed by a semiconductor region (lower electrode)extended from the drain region 14 of the switching TFT 201, the gateinsulating film 18, and a capacitor electrode (upper electrode) 1403.The capacitor electrode 1403 is formed at the same time as the gateelectrodes 19 a, 19 b, and 35 of the TFT.

[0239] A top view is shown in FIG. 15A. The cross sectional diagramtaken along the line A-A′ in the top view of FIG. 15A corresponds toFIG. 14. As shown in FIG. 15A, the capacitor electrode 1403 iselectrically connected to the source region 31 of the current controlTFT through a connecting wiring 1404 which is electrically connected tothe capacitor electrode 1403. Note that the connection wiring 1404 isformed at the same time as the source wirings 21 and 36, and the drainwirings 22 and 37. Furthermore, FIG. 15B shows the circuit constitutionof the top view shown in FIG. 15A.

[0240] Note that the constitution of embodiment 8 can be freely combinedwith the constitution of any of embodiments 1 to 7. In other words, onlythe storage capacitor is formed within the pixel, no limitations areadded with regard to the TFT structure or the EL layer materials.

[0241] Embodiment 9

[0242] Laser crystallization is used as the means of forming thecrystalline silicon film 302 in embodiment 1, and a case of using adifferent means of crystallization is explained in embodiment 9.

[0243] After forming an amorphous silicon film in embodiment 9,crystallization is performed using the technique recorded in JapanesePatent Application Laid-open No. Hei 7-130652. The technique recorded inthe above patent application is one of obtaining a crystalline siliconfilm having good crystallinity by using an element such as nickel as acatalyst for promoting crystallization.

[0244] Further, after the crystallization process is completed, aprocess of removing the catalyst used in the crystallization may beperformed. In this case, the catalyst may be gettered using thetechnique recorded in Japanese Patent Application Laid-open No. Hei10-270363 or Japanese Patent Application Laid-open No. Hei 8-330602.

[0245] In addition, a TFT may be formed using the technique recorded inthe specification of Japanese Patent Application No. Hei 11-076967 bythe applicant of the present invention.

[0246] The processes of manufacturing shown in embodiment 1 are oneembodiment of the present invention, and provided that the structure ofFIG. 1 or of FIG. 5C of embodiment 1 can be realized, then othermanufacturing process may also be used without any problems, as above.

[0247] Note that it is possible to freely combine the constitution ofembodiment 9 with the constitution of any of embodiments 1 to 8.

[0248] Embodiment 10

[0249] In driving the EL display device of the present invention, analogdriving can be performed using an analog signal as an image signal, anddigital driving can be performed using a digital signal.

[0250] When analog driving is performed, the analog signal is sent to asource wiring of a switching TFT, and the analog signal, which containsgray scale information, becomes the gate voltage of a current controlTFT. The current flowing in an EL element is then controlled by thecurrent control TFT, the EL element emitting intensity is controlled,and gray scale display is performed. In this case, it is preferable tooperate the current control TFT in a saturation region. In other words,it is preferable to operate the TFT within the conditions of|V_(ds)|>|V_(gs)−V_(th)|. Note that V_(ds) is the voltage differencebetween a source region and a drain region, V_(gs) is the voltagedifference between the source region and a gate electrode, and V_(th) isthe threshold voltage of the TFT.

[0251] On the other hand, when digital driving is performed, it differsfrom the analog type gray scale display, and gray scale display isperformed by time division driving (time ratio gray scale driving) orsurface area ratio gray scale driving. Namely, by regulating the lengthof the emission time or the ratio of emitting surface area, color grayscales can be made to be seen visually as changing. In this case, it ispreferable to operate the current control TFT in the linear region. Inother words, it is preferable to operate the TFT within the conditionsof |V_(ds)|<|V_(gs)−V_(th)|.

[0252] The EL element has an extremely fast response speed in comparisonto a liquid crystal element, and therefore it is possible to have highspeed driving. Therefore, the EL element is one which is suitable fortime ratio gray scale driving, in which one frame is partitioned into aplural number of subframes and then gray scale display is performed.Furthermore, it has the advantage of the period of one frame beingshort, and therefore the amount of time for which the gate voltage ofthe current control TFT is maintained is also short, and a storagecapacitor can be made smaller or eliminated.

[0253] The present invention is a technique related to the elementstructure, and therefore any method of driving it may thus be used.

[0254] Embodiment 11

[0255] In embodiment 11, examples of the pixel structure of the ELdisplay device of the present invention are shown in FIGS. 21A and 21B.Note that in embodiment 11, reference numeral 4701 denotes a sourcewiring of a switching TFT 4702, reference numeral 4703 denotes a gatewiring of the switching TFT 4702, reference numeral 4704 denotes acurrent control TFT, 4705 denotes an electric current supply line, 4706denotes a power source control TFT, 4707 denotes a power source controlgate wiring, and 4708 denotes an EL element. Japanese Patent ApplicationNo. Hei 11-341272 may be referred to regarding the operation of thepower source control TFT 4706.

[0256] Further, in embodiment 11 the power source control TFT 4706 isformed between the current control TFT 4704 and the EL element 4708, buta structure in which the current control TFT 4704 is formed between thepower source control TFT 4706 and the EL element 4708 may also be used.In addition, it is preferable for the power source control TFT 4706 tohave the same structure as the current control TFT 4704, or for both tobe formed in series by the same active layer.

[0257]FIG. 21A is an example of a case in which the electric currentsupply line 4705 is common between two pixels. Namely, this ischaracterized in that the two pixels are formed having linear symmetryaround the electric current supply line 4705. In this case, the numberof electric current supply lines can be reduced, and therefore the pixelportion can be made even more high precision.

[0258] Furthermore, FIG. 21B is an example of a case in which anelectric current supply line 4710 is formed parallel to the gate wiring4703, and in which a power source control gate wiring 4711 is formedparallel to the source wiring 4701. Note that in FIG. 23B, the structureis formed such that the electric current supply line 4710 and the gatewiring 4703 do not overlap, but provided that both are wirings formed ondifferent layers, then they can be formed to overlap, sandwiching aninsulating film. In this case, the exclusive surface area of theelectric current supply line 4710 and the gate wiring 4703 can beshared, and the pixel section can be made even more high precision.

[0259] Embodiment 12

[0260] In embodiment 12, examples of the pixel structure of the ELdisplay device of the present invention are shown in FIGS. 22A and 22B.Note that in embodiment 12, reference numeral 4801 denotes a sourcewiring of a switching TFT 4802, reference numeral 4803 denotes a gatewiring of the switching TFT 4802, reference numeral 4804 denotes acurrent control TFT, 4805 denotes an electric current supply line, 4806denotes an erasure TFT, 4807 denotes an erasure gate wiring, and 4808denotes an EL element. Japanese Patent Application No. Hei 11-338786 maybe referred to regarding the operation of the erasure TFT 4806.

[0261] The drain of the erasure TFT 4806 is connected to a gate of thecurrent control TFT 4804, and it becomes possible to forcibly change thegate voltage of the current control TFT 4804. Note that an n-channel TFTor a p-channel TFT may be used for the erasure TFT 4806, but it ispreferable to make it the same structure as the switching TFT 4802 sothat the off current value can be made smaller.

[0262]FIG. 22A is an example of a case in which the electric currentsupply line 4805 is common between two pixels. Namely, this ischaracterized in that the two pixels are formed having linear symmetryaround the electric current supply line 4805. In this case, the numberof electric current supply lines can be reduced, and therefore the pixelsection can be made even more high precision.

[0263] In addition, FIG. 22B is an example of a case in which anelectric current supply line 4810 is formed parallel to the gate wiring4803, and in which an erasure gate wiring 4811 is formed parallel to thesource wiring 4801. Note that in FIG. 22B, the structure is formed suchthat the electric current supply line 4810 and the gate wiring 4803 donot overlap, but provided that both are wirings formed on differentlayers, then they can be formed to overlap, sandwiching an insulatingfilm. In this case, the exclusive surface area of the electric currentsupply line 4810 and the gate wiring 4803 can be shared, and the pixelsection can be made even more high precision.

[0264] Embodiment 13

[0265] The EL display device of the present invention may have astructure in which several TFTs are formed within a pixel. Inembodiments 11 and 12, examples of forming three TFTs are shown, butfrom 4 to 6 TFTs may also be formed. It is possible to implement thepresent invention without placing any limitations on the structure ofthe pixels of the EL display device.

[0266] Embodiment 14

[0267] An example of using a p-channel TFT as the current control TFT202 of FIG. 1 is explained in embodiment 14. Note that other portionsare the same as those of FIG. 1, and therefore a detailed explanation ofthe other portions is omitted.

[0268] A cross sectional structure of the pixel of embodiment 14 isshown in FIG. 23. Embodiment 1 may be referred to for a method ofmanufacturing the p-channel TFT used in embodiment 14. An active layerof the p-channel TFT comprises a source region 2801, a drain region2802, and a channel forming region 2803, and the source region 2801 isconnected to the source wiring 36, and the drain region 2802 isconnected to the drain wiring 37.

[0269] For cases in which the anode of an EL element is connected to thecurrent control TFT, it is preferable to use the p-channel TFT as thecurrent control TFT.

[0270] Note that it is possible to implement the constitution ofembodiment 14 by freely combining it with the constitution of any ofembodiments 1 to 13.

[0271] Embodiment 15

[0272] By using an EL material in which phosphorescence from a tripletstate exciton can be utilized in light emission in embodiment 15, theexternal emission quantum efficiency can be increased by a great amount.By doing so, it becomes possible to make the EL element into a low powerconsumption, long life, and low weight EL element.

[0273] Reports of utilizing triplet state excitons and increasing theexternal emission quantum efficiency is shown in the following papers.

[0274] Tsutsui, T., Adachi, C., and Saito, S., Photochemical Processesin Organized Molecular Systems, Ed. Honda, K., (Elsevier Sci. Pub.,Tokyo, 1991), p. 437.

[0275] The molecular formula of the EL material (coumarin pigment)reported in the above paper is shown below.

[0276] Baldo, M. A., O'Brien, D. F., You, Y., Shoustikov, A., Sibley,S., Thompson, M. E., and Forrest, S. R., Nature 395 (1998) p. 151.

[0277] The molecular formula of the EL material (Pt complex) reported inthe above paper is shown below.

[0278] Baldo, M. A., Lamansky, S., Burrows, P. E., Thompson, M. E., andForrest, S. R., Appl. Phys. Lett., 75 (1999) p. 4.

[0279] Tsutui, T., Yang, M. J., Yahiro, M., Nakamura, K., Watanabe,T.,Tsuji, T., Fukuda, Y., Wakimoto, T., Mayaguchi, S., Jpn. Appl. Phys., 38(12B) (1999) L1502.

[0280] The molecular formula of the EL material (Ir complex) reported inthe above paper is shown below.

[0281] Provided that the phosphorescence emission from triplet stateexcitons can be utilized, then in principle it is possible to realize anexternal emission quantum efficiency which is 3 to 4 times higher thanthat for cases of using the fluorescence emission from singlet stateexcitons. Note that it is possible to implement the constitution ofembodiment 15 by freely combining it with the constitution of any ofembodiments 1 to 14.

[0282] Embodiment 16

[0283] In embodiment 1 it is preferable to use an organic EL material asan EL layer, but the present invention can also be implemented using aninorganic EL material. However, current inorganic EL materials have anextremely high driving voltage, and therefore a TFT which has voltageresistance characteristics that can withstand the driving voltage mustbe used in cases of performing analog driving.

[0284] Alternatively, if inorganic EL materials having lower drivingvoltages than conventional inorganic EL materials are developed, then itis possible to apply them to the present invention.

[0285] Further, it is possible to freely combine the constitution ofembodiment 16 with the constitution of any of embodiments 1 to 14.

[0286] Embodiment 17

[0287] An active matrix type EL display device (EL module) formed byimplementing the present invention has superior visibility in brightlocations in comparison to a liquid crystal display device because it isa self-emitting type device. It therefore has a wide range of uses as adirect-view type EL display (indicating a display incorporating an ELmodule).

[0288] Note that a wide viewing angle can be given as one advantagewhich the EL display has over a liquid crystal display. The EL displayof the present invention may therefore be used as a display (displaymonitor) having a diagonal equal to 30 inches or greater (typicallyequal to 40 inches or greater) for appreciation of TV broadcasts bylarge screen.

[0289] Further, not only can it be used as an EL display (such as apersonal computer monitor, a TV broadcast reception monitor, or anadvertisement display monitor), it can be used as a display for variouselectronic devices.

[0290] The following can be given as examples of such electronicdevices: a video camera; a digital camera; a goggle type display (headmounted display); a car navigation system; a personal computer; aportable information terminal (such as a mobile computer, a mobiletelephone, or an electronic book); and an image playback device using arecording medium (specifically, a device which performs playback of arecording medium and is provided with a display which can display thoseimages, such as a compact disk (CD), a laser disk (LD), or a digitalvideo disk (DVD)). Examples of these electronic devices are shown inFIGS. 16A to 16F.

[0291]FIG. 16A is a personal computer, comprising a main body 2001, acasing 2002, a display portion 2003, and a keyboard 2004. The presentinvention can be used in the display portion 2003.

[0292]FIG. 16B is a video camera, comprising a main body 2101, a displayportion 2102, an audio input portion 2103, operation switches 2104, abattery 2105, and an image receiving portion 2106. The present inventioncan be used in the display portion 2102.

[0293]FIG. 16C is a goggle display, comprising a main body 2201, adisplay portion 2202, and an arm portion 2203. The present invention canbe used in the display portion 2202.

[0294]FIG. 16D is a mobile computer, comprising a main body 2301, acamera portion 2302, an image receiving portion 2303, operation switches2304, and a display portion 2305. The present invention can be used inthe display portion 2305.

[0295]FIG. 16E is an image playback device (specifically, a DVD playbackdevice) provided with a recording medium, comprising a main body 2401, arecording medium (such as a CD, an LD, or a DVD) 2402, operationswitches 2403, a display portion (a) 2404, and a display portion (b)2405. The display portion (a) is mainly used for displaying imageinformation, and the image portion (b) is mainly used for displayingcharacter information, and the present invention can be used in theimage portion (a) and in the image portion (b). Note that the presentinvention can be used as an image playback device provided with arecording medium in devices such as a CD playback device and gameequipment.

[0296]FIG. 16F is an EL display, containing a casing 2501, a supportstand 2502, and a display portion 2503. The present invention can beused in the display portion 2503. The EL display of the presentinvention is especially advantageous for cases in which the screen ismade large, and is favorable for displays having a diagonal greater thanor equal to 10 inches (especially one which is greater than or equal to30 inches).

[0297] Furthermore, if the emission luminance of EL materials becomeshigher in future, then it will become possible to use the presentinvention in a front type or a rear type projector.

[0298] The above electronic devices are becoming more often used todisplay information provided through an electronic transmission circuitsuch as the Internet or CATV (cable television), and in particular,opportunities for displaying animation information are increasing. Theresponse speed of EL materials is extremely high, and therefore ELdisplays are suitable for performing this type of display.

[0299] The emitting portion of the EL display device consumes power, andtherefore it is preferable to display information so as to have theemitting portion become as small as possible. Therefore, when using theEL display device in a display portion which mainly displays characterinformation, such as a portable information terminal, in particular, aportable telephone of a car audio system, it is preferable to drive itby setting non-emitting portions as background and forming characterinformation in emitting portions.

[0300]FIG. 20A is a portable telephone, comprising a main body 2601, anaudio output portion 2602, an audio input portion 2603, a displayportion 2604, operation switches 2605, and an antenna 2606. The ELdisplay device of the present invention can be used in the displayportion 2604. Note that by displaying white characters in a blackbackground in the display portion 2604, the power consumption of theportable telephone can be reduced.

[0301]FIG. 20B is an on-board audio system (car audio system),containing a main body 2701, a display portion 2702, and operationswitches 2703 and 2704. The EL display device of the present inventioncan be used in the display portion 2702. Furthermore, an on-board audiosystem is shown in embodiment 17, but a desktop type audio system mayalso be used. Note that by displaying white characters in a blackbackground in the display portion 2702, the power consumption can bereduced.

[0302] The range of applications of the present invention is thusextremely wide, and it is possible to apply the present invention toelectronic devices in all fields. Furthermore, the electronic devices ofembodiment 17 can be realized by using any constitution of anycombination of embodiments 1 to 16.

[0303] By using the present invention the EL elements are prevented fromdegrading by moisture and heat. Further, giving bad influence on TFTcharacteristic by diffusion of alkaline metals from the EL layer isprevented. As a result, the operating performance and the reliability ofthe EL display devices can be greatly improved.

[0304] Further, it becomes possible to produce application products(electronic devices) having good image quality and durability(reliability is high) by comprising such EL display device as a display.

What is claimed is:
 1. An electro-optical device wherein an EL elementis in contact with an insulating film including at least one of theelements selected from a group consisting of B (boron), C (carbon), N(nitrogen) and at least one of the elements selected from a groupconsisting of Al (aluminum), Si (silicon) and P (phosphorus).
 2. Anelectro-optical device wherein an EL element is in contact with aninsulating film comprising one selected from a group consisting ofaluminum nitride, silicon carbide, silicon nitride, boron nitride, boronphosphate and aluminum oxide.
 3. An electro-optical device wherein an ELelement is in contact with an insulating film comprising Si, Al, N, Oand M where M is a rare earth element, preferably one selected from agroup consisting of Ce (cerium), Yb (ytterbium), Sm (samarium), Er(erbium), Y (yttrium), (La) lanthanum, Gd (gadolinium), Dy (dysprosium)and Nd (neodymium).
 4. An electro-optical device wherein an EL elementis in contact with a carbon film.
 5. An electro-optical device accordingto claim 4 wherein the carbon film is a diamond film or adiamond-like-carbon film.
 6. An electro-optical device in which an ELelement is enclosed by insulating films that comprise an elementselected from a group consisting of B (boron), C (carbon) and N(nitrogen) and an element selected from a group consisting of Al(aluminum), Si (silicon) and P (phosphorus).
 7. An electro-opticaldevice wherein an EL element is enclosed by insulating films thatcomprise one selected from a group consisting of aluminum nitride,silicon carbide, silicon nitride, boron nitride, boron phosphate andaluminum oxide.
 8. An electro-optical device wherein an EL element isenclosed by insulating films that comprise Si, Al, N, O and M where M isa rare earth element, preferably one selected from a group consisting ofCe (cerium), Yb (ytterbium), Sm (samarium), Er (erbium), Y (yttrium),(La) lanthanum, Gd (gadolinium), Dy (dysprosium) and Nd (neodymium). 9.An electro-optical device wherein an EL element is enclosed by carbonfilms.
 10. An electro-optical device according to claim 9 wherein thecarbon films are a diamond film or a diamond-like-carbon film.
 11. Adevice according to claim 1 wherein the EL element is electricallyconnected to a second TFT which has a gate electrically connected to afirst TFT.
 12. A device according to claim 2 wherein the EL element iselectrically connected to a second TFT which has a gate electricallyconnected to a first TFT.
 13. A device according to claim 3 wherein theEL element is electrically connected to a second TFT which has a gateelectrically connected to a first TFT.
 14. A device according to claim 4wherein the EL element is electrically connected to a second TFT whichhas a gate electrically connected to a first TFT.
 15. A device accordingto claim 5 wherein the EL element is electrically connected to a secondTFT which has a gate electrically connected to a first TFT.
 16. A deviceaccording to claim 6 wherein the EL element is electrically connected toa second TFT which has a gate electrically connected to a first TFT. 17.A device according to claim 7 wherein the EL element is electricallyconnected to a second TFT which has a gate electrically connected to afirst TFT.
 18. A device according to claim 8 wherein the EL element iselectrically connected to a second TFT which has a gate electricallyconnected to a first TFT.
 19. A device according to claim 9 wherein theEL element is electrically connected to a second TFT which has a gateelectrically connected to a first TFT.
 20. A device according to claim11 wherein the first TFT is a switching element and the second TFT is acurrent controlling element.
 21. A device according to claim 12 whereinthe first TFT is a switching element and the second TFT is a currentcontrolling element.
 22. A device according to claim 13 wherein thefirst TFT is a switching element and the second TFT is a currentcontrolling element.
 23. A device according to claim 14 wherein thefirst TFT is a switching element and the second TFT is a currentcontrolling element.
 24. A device according to claim 15 wherein thefirst TFT is a switching element and the second TFT is a currentcontrolling element.
 25. A device according to claim 16 wherein thefirst TFT is a switching element and the second TFT is a currentcontrolling element.
 26. A device according to claim 17 wherein thefirst TFT is a switching element and the second TFT is a currentcontrolling element.
 27. A device according to claim 18 wherein thefirst TFT is a switching element and the second TFT is a currentcontrolling element.
 28. A device according to claim 19 wherein thefirst TFT is a switching element and the second TFT is a currentcontrolling element.
 29. A device according to claim 1 wherein theinsulating film is disposed in a laminate with silicon oxide film,silicon nitride film or a silicon oxynitride film.
 30. A deviceaccording to claim 2 wherein the insulating film is disposed in alaminate with silicon oxide film, silicon nitride film or a siliconoxynitride film.
 31. A device according to claim 3 wherein theinsulating film is disposed in a laminate with silicon oxide film,silicon nitride film or a silicon oxynitride film.
 32. A deviceaccording to claim 4 wherein the insulating film is disposed in alaminate with silicon oxide film, silicon nitride film or a siliconoxynitride film.
 33. A device according to claim 5 wherein theinsulating film is disposed in a laminate with silicon oxide film,silicon nitride film or a silicon oxynitride film.
 34. A deviceaccording to claim 6 wherein the insulating film is disposed in alaminate with silicon oxide film, silicon nitride film or a siliconoxynitride film.
 35. A device according to claim 7 wherein theinsulating film is disposed in a laminate with silicon oxide film,silicon nitride film or a silicon oxynitride film.
 36. A deviceaccording to claim 8 wherein the insulating film is disposed in alaminate with silicon oxide film, silicon nitride film or a siliconoxynitride film.
 37. A device according to claim 9 wherein theinsulating film is disposed in a laminate with silicon oxide film,silicon nitride film or a silicon oxynitride film.
 38. A deviceaccording to claim 1 wherein the EL element is formed over a resin filmand an insulating film is disposed between the resin film and the ELelement.
 39. A device according to claim 2 wherein the EL element isformed over a resin film and an insulating film is disposed between theresin film and the EL element.
 40. A device according to claim 3 whereinthe EL element is formed over a resin film and an insulating film isdisposed between the resin film and the EL element.
 41. A deviceaccording to claim 4 wherein the EL element is formed over a resin filmand an insulating film is disposed between the resin film and the ELelement.
 42. A device according to claim 5 wherein the EL element isformed over a resin film and an insulating film is disposed between theresin film and the EL element.
 43. A device according to claim 6 whereinthe EL element is formed over a resin film and an insulating film isdisposed between the resin film and the EL element.
 44. A deviceaccording to claim 7 wherein the EL element is formed over a resin filmand an insulating film is disposed between the resin film and the ELelement.
 45. A device according to claim 8 wherein the EL element isformed over a resin film and an insulating film is disposed between theresin film and the EL element.
 46. A device according to claim 9 whereinthe EL element is formed over a resin film and an insulating film isdisposed between the resin film and the EL element.
 47. An electronicdevice which comprises an electro-optical device according to claim 1.48. A device according to claim 11 wherein the first TFT and the secondTFT are disposed on an insulating film, wherein the insulating film isan insulating film that comprises at least an element selected from agroup consisting of B (boron), C (carbon) and N (nitrogen) and anelement selected from a group consisting of Al (aluminum), Si (silicon)and P (phosphorus), or an insulating film that comprises Si, Al, N, Oand M where M is a rare earth element preferably one selected from agroup consisting of Ce (cerium), Yb (ytterbium), Sm (samarium), Er(erbium), Y (yttrium), (La) lanthanum, Gd (gadolinium), Dy (dysprosium)and Nd (neodymium).
 49. A method for manufacturing an electro-opticaldevice comprising the steps of: forming a plurality of TFTs over asubstrate; forming an insulating film that cover the plurality of TFTs;forming a passivation film over the insulating film; and forming an ELelement over the passivation film.
 50. A method according to claim 49wherein the insulating film comprises a resin film.
 51. A methodaccording to claim 49 wherein the passivation film comprises aninsulating film that comprises at least an element selected from a groupconsisting of B (boron), C (carbon) and N (nitrogen) and an elementselected from a group consisting of Al (aluminum), Si (silicon) and P(phosphorus), or an insulating film that comprises Si, Al, N, O and Mwhere M is a rare earth element preferably one selected from a groupconsisting of Ce (cerium), Yb (ytterbium), Sm (samarium), Er (erbium), Y(yttrium), (La) lanthanum, Gd (gadolinium), Dy (dysprosium) and Nd(neodymium).
 52. A method for manufacturing an electro-optical devicecomprising the steps of: forming a plurality of TFTs over a substrate;forming an insulating film that covers the plurality of TFTs; forming afirst passivation film over the insulating film; forming an EL elementover the first passivation film; and forming a second passivation filmthat covers the EL element, wherein the EL element is enclosed by thefirst passivation film and the second passivation film.
 53. A methodaccording to claim 52 wherein the insulating film comprises a resinfilm.
 54. A method according to claim 52 wherein the first passivationfilm and the second passivation film comprises at least an elementselected from a group consisting of B (boron), C (carbon) and N(nitrogen) and an element selected from a group consisting of Al(aluminum), Si (silicon) and P (phosphorus).
 55. A method according toclaim 52 wherein the first passivation film and the second passivationfilm comprises Si, Al, N, O and M where M is a rare earth elementpreferably one selected from a group consisting of Ce (cerium), Yb(ytterbium), Sm (samarium), Er (erbium), Y (yttrium), (La) lanthanum, Gd(gadolinium), Dy (dysprosium) and Nd (neodymium).
 56. A method accordingto claim 49 further comprising a step of forming an insulating film thatcomprises at least an element selected from a group consisting of B(boron), C (carbon) and N (nitrogen) and an element selected from agroup consisting of Al (aluminum), Si (silicon) and P (phosphorus),between the substrate and the plurality of TFTs.
 57. A method accordingto claim 52 further comprising a step of forming an insulating film thatcomprises at least an element selected from a group consisting of B(boron), C (carbon) and N (nitrogen) and an element selected from agroup consisting of Al (aluminum), Si (silicon) and P (phosphorus),between the substrate and the plurality of TFTs.
 58. A method accordingto claim 49 further comprising a step of forming an insulating film thatcomprises Si, Al, N, O and M where M is a rare earth element preferablyone selected from a group consisting of Ce (cerium), Yb (ytterbium), Sm(samarium), Er (erbium), Y (yttrium), (La) lanthanum, Gd (gadolinium),Dy (dysprosium) and Nd (neodymium), between the substrate and theplurality of TFTs.
 59. A method according to claim 52 further comprisinga step of forming an insulating film that comprises Si, Al, N, O and Mwhere M is a rare earth element preferably one selected from a groupconsisting of Ce (cerium), Yb (ytterbium), Sm (samarium), Er (erbium), Y(yttrium), (La) lanthanum, Gd (gadolinium), Dy (dysprosium) and Nd(neodymium), between the substrate and the plurality of TFTs.